1. Field of the Invention
The present invention relates to complex-shaped carbon fiber structural parts and components, such as those used on bicycles and bicycle suspension systems, and their method of manufacture. In particular, the invention relates to three-dimensional parts and structural components made of composite carbon epoxy fiber bundles surrounded by a unidirectional carbon fiber rope.
2. Discussion of the Related Art
Composite fiber materials have been utilized in place of metal for constructing structural frames and frame members in a number of applications. Composite fiber materials generally have a lower density, higher specific strength and stiffness, and better dampening qualities than metals. Composite fiber materials therefore normally provide an increase in strength and stiffness with a reduction in weight, as compared to similar structural members made of steel and aluminum alloys and other metals. Because of the natural desire to reduce the weight of bicycles, composite fiber materials have been specifically used in the manufacture of bicycle frames.
One highly successful line of composite fiber bicycle frames is the Optimum Compaction Low Void (OCLV) series manufactured by the Trek Bicycle Corporation. The frame for a Trek OCLV 5500 bicycle, for example, is formed by joining a set of composite fiber tubes to a set of composite fiber lugs. The tubes are those portions of the frame that form the top tube, down lube, seat tube, chain stays and seat stays. The lugs are the irregularly shaped portions of the frame that form the head lug, seat lug and bottom bracket lug. The lugs are preformed and pre-cured articles fabricated from a composite fiber material comprised of overlaid layers of unidirectional carbon fibers embedded in an epoxy resin. Several layers of material are stacked on top of each other so that the fibers of adjacent layers cross over one another. The stacks of unidirectional fibers are cut into shapes called preforms for molding into a particular lug. The preforms are placed in a mold and arranged around an inflatable bladder. The assembly of preforms is then heated and cured, with the bladder pressurized for urging the respective preforms into the shape of the mold. This method of fabrication provides a high laminate compaction having low voids, which results in a strong, uniform, thin walled, tubular lug. The composite fiber tubes may be formed by a similar method. The separate tubes and lugs are then glued together to construct the frame. Further details of this method of making an all-composite bicycle frame are disclosed in U.S. Pat. Nos. 5,624,519 and 6,270,104 assigned to the Trek Bicycle Corporation.
The above-described method for making composite lugs has also been used to make larger frame members, sometimes called large lugs, such as the Y-shaped frame shown in U.S. Pat. Nos. 5,685,553 and 6,109,638 also assigned to the Trek Bicycle Corporation. The Y-shaped frame is identified as reference numeral 12 in FIG. 1 of the '553 patent, and identified with reference numeral 20 in FIG. 1 of the '638 patent.
The carbon fiber structures and the methods of manufacture discussed above relate, as mentioned, to the bicycle frame, which is the largest and typically heaviest portion of a bicycle. However, there are a number of other components to a bicycle which are commonly made of metal. It is desirable to also make those other components as light in weight as possible. One method to make parts using carbon fibers has been to use a material known as a short fiber composite material consisting of random chopped fibers. The material, referred to in the composite industry as sheet molding compound, comes in a roll of sheet material of the randomly chopped fibers. The chopped fiber material is placed into a mold under heat and compression, and formed in a manner much like an injection molding process. Upon heating, the short fibers which are embedded in an epoxy resin essentially flow to take on the form of the mold. Unfortunately, structural components made solely of short fiber composite materials have not exhibited sufficient strength and durability, particularly in the rugged environments found in bicycle racing and mountain bicycling. Such parts have been prone to failure and cracking.
Of course, in the field of bicycles, and especially in the field of bicycle racing, there is a never-ending desire to build ever-lighter bicycles and bicycle components.